By Thomas Ferraro and Richard Cowan

WASHINGTON (Reuters) - The Congress fell to new depths of public disapproval in the past two years, yet no big shake-up of the Senate or House of Representatives is expected in Tuesday's general election.

With days remaining before the vote, Democrats were expected to fend off what is seen as a fading Republican challenge for control of the Senate, with a 50-50 tie also a possibility.

The most likely victor is the status quo, with neither Democrats nor Republicans on track to win the super-majority necessary to quickly advance legislation, leaving each party capable of blocking almost anything they please.

Coupled with a House of Representatives that is expected to stay in Republican hands, the Congress to be sworn in next January to grapple with daunting budget and tax controversies may look an awful lot like the current, deeply divided legislature.

Whether it has any more success carrying out its basic responsibilities is an open question. Scholars of Congress generally regard the current version as one of least productive - and most destructive - in modern history.

It has failed to complete its most fundamental task of appropriating money to run the government, except on a temporary basis. The showdown in 2011 over the debt ceiling between Republicans and Democrats resulted in a downgrading of the U.S. government's creditworthiness.

In return, the public has disapproved of Congress at record levels, with the lowest rating of 10 percent coming in August, according to a Gallup poll.

Democrats have held the majority in the Senate since 2007.

For months, Democrats expressed confidence that they could maintain their 53-47 edge in Tuesday's elections, when one-third of the chamber's 100 seats will be in play.

Their optimism was bolstered by what many perceived as Republican missteps this year: Romney's poor early performance at the top of the Republican ticket coupled with the perception that some candidates, such as Tea Party activist Richard Mourdock in Indiana, could be too conservative for their states.

Mourdock now trails his Democratic challenger by 11 points, according to a new Howey-DePauw poll, offering a strong hint that Republicans will lose a seat that was first won in 1976 by one of their few remaining moderates, Senator Richard Lugar.

Some Republican candidates may have turned off voters with inflammatory comments on the campaign trail. Todd Akin's late summer musings on "legitimate rape" complicated what was considered to be his clear shot at unseating Democratic U.S. Senator Claire McCaskill in Missouri.

In addition, Republicans suffered a blow when Olympia Snowe, the popular moderate from Maine, decided to retire, opening a path for the state's former governor, Angus King, to run as an independent who likely would align himself with Democrats if elected.

The non-partisan Rothenberg Political Report predicts that Republicans will have a net gain of no more than three seats, one short of the number needed to ensure control.

Rothenberg sees three Senate races as real toss-ups: Montana, Virginia and Wisconsin, all of which are currently held by Democrats.

Plenty of other races are too close to call, including Massachusetts, where Democrat Elizabeth Warren has been gaining momentum against Republican incumbent Scott Brown.

THE DEEP DIVIDE

Still, with the presidential race and many of the 33 Senate races tightening up, Republicans in the final days of the campaigns have become more encouraged about their prospects of taking over the chamber.

One Senate Republican leadership aide pointed to narrowing presidential and Senate races in Pennsylvania as giving hope for a Republican takeover of the chamber.

Larry Sabato, head of the University of Virginia's Center for Politics, was less convinced. "A 50-50 Senate is certainly possible," he said, adding that Democrats "have a decent shot at 52 or even 53" seats.

That would be a reversal of last year's conventional wisdom. Throughout 2011, political junkies looked at the sluggish U.S. economy under Obama, did some simple math and concluded that in 2013, Republican Senator Mitch McConnell would finally win his quest to hold the "majority leader" title.

The simple math is that in this election, Democrats are defending 21 seats, plus two more that are now controlled by independents who generally side with them.

Republicans, with just 10 seats to defend, have more opportunities to pick up seats and fewer chances to lose them.

"On the whole, Democrats have done much better than they looked likely to do a year ago," Sabato said. "This election could have been a disaster for Senate Democrats, but it doesn't look to be now." Continued...